Transducer for electronically-controlled timepiece



Nov. 30, 1965 w. o. BENNETT ETAL TRANSDUCER FOR ELECTRONICALLY-CONTROLLED TIMEPIECE Original Filed Jan. 19, 1961 Zlq Zle Zlc,

INVENTORS Mum O. BEN/V677 MLLIAM M Mun-E? BY 656197- Vq/v I/IIMFTEIY me/v57 United States Patent 3,221,190 TRANSDUCER FOR ELECTRONICALLY- CONTROLLED TIMEPIECE William 0. Bennett, Bayside, N.Y., and William W. Mutter, Paramus, and Egbert Van Haaften, Cluster, N.J., assignors to Bulova Watch Company, Inc., New York, N.Y., a corporation of New York Original application Jan. 19, 1961, Ser. No. 89,896. Di-

vided and this application Aug. 19, 1963, Ser. No. 302,954

4 Claims. (Cl. 310-25) This invention relates generally to electronicallycontrolled timepieces which incorporate electromagnetically-actuated tuning forks, and more particularly to improved transducer structures therefor. This application is a division of our copending application Serial No. 89,896, filed January 19, 1961, now abandoned.

In ordinary electric watches, make-and-break contacts are mechanically operated by the swinging of the balance wheel. Each time these contacts close, battery current flows in a coil or coils to electro-magnetically impulse the balance wheel. This mechanically operated make-andbreak contact system is subject to Wear and also to deterioration and contamination of the delicate contact points which must open and close an electric circuit without fail 216,000 times a day. The slightest sparking will cause rapid deterioration of these contacts and early failure of the watch.

The present invention does away with a balance wheel and escapement as well as make-and-break contacts and makes use of a timekeeping tuning fork which is pulsed electromagnetically by means of a transistor circuit. It constitutes an improvement over timepieces of the type disclosed in the copending applications Serial No. 665,480, filed June 13, 1957, entitled Electronically-Controlled Timepiece, issued February 14, 1961, as Patent No. 2,971,323, and in Serial No. 584,709, filed May 14, 1956, entitled Electrical Timepiece, issued November 22, 1960, as Patent No. 2,960,817.

In said copending applications there are disclosed novel timepieces including a self-sufficient timekeeping standard formed by a tuning fork having a predetermined natural frequency and a battery-energized transistorized drive circuit to sustain the vibratory motion of the fork. This motion is transferred to a rotary movement including the usual gear train and dial pointers by means of a pawl attached to one tine of the fork, the pawl advancing a ratchet wheel which drives the gear train.

When the timepiece is to be confined Within a watch casing or in a small chamber of similar dimensions, it is vitally important that the electrical and mechanical efficiency of the system be of an exceptionally high order. Otherwise, any loss of energy which in a larger scale device may be negligible, can give rise to serious drawbacks in the more compact structure.

It must be borne in mind that the sole source of energy for the timepiece is a single miniature battery cell. Thus any factor which dissipates energy or reduces efiiciency not only cuts down the useful battery life but also creates operating difiiculties. Also of importance is that maximum use be made of all available space and that the transducers which actuate the fork operate at optimum elliciency.

The main object of this invention is to provide a magnetic transducer of exceptional efliciency for actuating a tuning fork in an electronic watch of the above-described type. The construction of the magnetic element and of the coils constituting the transducer are such as to realize an optimum relationship between flux denstiy and the number of coil turns.

For a better understanding of the invention as well as other objects and further features thereof, reference is made to the following detailed description to be read in conjunction with the accompanying drawings wherein like components in the several figures are identified by like reference numerals.

In the drawings:

FIG. 1 is a schematic representation, in perspective, of the basic components of an electronic timepiece in accordance with the invention.

FIG. 2 is a separate view of the tuning fork structure showing the transducer partly in section.

FIG. 3 is a side view of the transducer.

Referring now to the drawings and more particularly to FIG. 1, the major components of a timepiece in accordance with the invention are a timekeeping standard constituted by a tuning fork 10 and an electronic drive circuit 11 therefor, a rotary movement of conventional design including a gear train 12 for turning the hands of the timepiece, and a motion transformer including an index wheel 13 operatively intercoupling the fork 10 and the rotary movement 12 and acting to convert the vibratory action of the fork into rotary motion. The tuning fork has no pivots or bearings and its timekeeping action is therefore independent of the effects of friction.

All of the electrical components of the drive circuit are mounted on the unitized sub-assembly units or modules F and F attached to a disc-shaped metallic pillar plate 14 which may be supported within a watch casing of standard design or within any other type of housing, depending on the use to which the timepiece is put. Electronic circuit 11 is constituted by a transistor TR having a base B, a collector C, and an emitter E, a resistance-capacitance biasing network R-C, and a by-pass capacitor C to prevent parasitic oscillations of the circuit. The electronic circuit 11 is energized by a voltage source in the form of a battery V.

Tuning fork 10 is provided with a pair of flexible tines 15 and 16 interconnected by a relatively inflexible base 17, the base being provided with an upwardly extending stem 18 secured to the pillar plate by suitable screws 19 and 20. The central area of the pillar plate is cut out to permit unobstructed vibration of the tines.

The tuning fork is actuated by means of a first transducer T constituted by a magnetic element 21 secured to the free end of tine 15, the element coacting with a drive coil 22, and a phase sensing coil 23. Drive coil 22 is wound on an open ended tubular carrier 24 affixed to a sub-assembly mounting form F which is secured to pillar plate 14. Coils 22 and 23 may be wound in juxtaposed relation on carrier 24 or the phase sensing coil 23 may be Wound over drive coil 22.

A second transducer T is provided constituted by a magnetic element 25 secured to the free end of tine 16 and coacting with a drive coil 26 wound on a tubular carrier 27.

In a practical embodiment the two transducer coil structures are 0.15 inch long and 0.18 inch in diameter. Drive coil 26 of transducer T has about 8000 turns of .0006 each wire, whereas in transducer T drive coil 22 has about 6000 turns and phase sensing coil about 2000 turns of the same wire. Thus the two transducers bear the same number of turns.

The two transducers T and T are of like design except that an additional coil is provided in transducer T The construction and behavior of the transducers are similar to that of a dynamic speaker of the permanent magnet type save that the moving element is the magnet and not the coil.

As shown for transducer T in FIGS. 2 and 3, the magnetic element 21 is constituted by a cylindrical cup 21a of magnetic material, such as iron, and a permanent magnet rod 211) coaxially mounted therein. The magnet 21b, which may be made for example of Alnico, is supported on the end wall of the cup to provide a magnetic circuit in which the lines of magnetic flux extend across the annular air gap 210 defined by the inner magnet and the surrounding cylinder. The magnet 21b is tapered to assume a frustoconical shape, whereby the cross-sectional area of the air gap at the mouth of the cup is relatively large.

As best seen in FIG. 3, cylindrical cup 215; is cut out longitudinally along diametrically opposed planes to form slots 21d and 21s. This effects a substantial reduction in the transducer dimension with relatively little flux leakage. The cutouts act to reduce the space occupied by the cups in depth within the casing and make possible a more compact construction of the timepiece. The slots also prevent so-called dash pot effects resulting from air compression of the magnet and cup assembly. Such damping is avoided by the slot openings and also by the openings in the tubular carrier.

It will be seen that fixed carrier 23 for supporting the drive coil 22 is horn shaped and is dimensioned to com plement the tapered magnet 21b. The carrier 23 and the drive coil supported thereon are received Within the annular gap 21c and are spaced both from the magnet and the surrounding cylinder, whereby the magnetic element is free to reciprocate axially relative to the fixed coil.

It will also be noted that the coil 22 wound about carrier 23 is tapered in cross-section so that the greatest number of turns is concentrated at the mouth of the air gap 210, the least number of turns being located well within the interior of the magnetic element. Since the magnetomotive force produced by the transducer at the fixed frequency and amplitude is the product of coil turns multiplied by flux density, optimum results are obtained by the structure shown herein, where the greatest number of turns is found at the point of maximum flux density.

In operation, an energizing pulse applied to the drive coils of the transducer will cause an axial thrust on the associated magnetic element in a direction determined by the polarity of the pulse in relation to the polarization of the permanent magnet and to an extent depending on the energy of the pulse. Since the magnetic element is attached to a tine of the tuning fork, the thrust on the element acts mechanically to excite the fork into vibration.

The vibratory action of the fork and the concomitant movement of the magnetic element induces a back in the drive coil, and in the case of the transducer T in the phase-sensing coil as well. Since the magnetic element reciprocates in accordance with the vibratory action of the tuning fork, the back will take the form of an alternating voltage whose frequency corresponds to that of the fork.

Three functions are served by the transducers. They drive the tuning fork by converting pulses of current delivered to the coils to mechanical pulses. The control the amplitude of the tuning fork by sensing the alternating voltage induced during each cycle, and they control the instant during the cycle when the driving pulse is to be delivered to the coils.

While there has been shown a preferred embodiment of the invention, it will be manifest that many changes may be made therein without departing from the essential features of the invention as defined in the annexed claims.

What is claimed is:

1. A transducer comprising a magnetic element formed by a cylinder having a magnetic rod supported coaxially therein to define an air gap, and a multi-turn cylindrical coil received within the annular space between said rod and cylinder, said rod being tapered and said coil being similarly tapered to produce the greatest number of turns within said air gap at the position of maximum flux density, said magnet element being movable relative to said coil.

2. An electromagnetically-actuated vibrator comprising a tuning fork having a pair of tines, and means for actuating said fork including a transducer constituted by a magnetic element attached to one of said tines and formed by a cylinder having a magnetic rod supported coaxially therein to define an air gap, a fixedly supported multiturn cylindrical coil received within the annular space between said and cylinder, said rod being tapered and said coil being similarly tapered to locate the greatest number of turns within said air gap at the position of maximum flux density.

3. An electromagnetically-actuated vibrator comprising a tuning fork having a pair of tines, and means for actuating said fork including a transducer constituted by a magnetic element attached to one of said tines and formed by a cylindrical cup having a magnetic rod supported coaxially therein to define an air gap at the mouth of said cup, at fixedly-supported multi-turn cylindrical coil received within the annular space between said rod and cylinder, said element vibrating axially relative to said coil, said rod being tapered and said coil being similarly tapered to produce the greatest number of turns within said air gap at the position of maximum flux density.

4. A vibrator as set forth in claim 3, wherein said coil is wound about a tapered carrier which is telescoped within said annular space.

References Cited by the Examiner UNITED STATES PATENTS 3,149,274 9/1964 Hetzel 3l0132 X ORIS L. RADER, Primary Examiner. 

3. AN ELECTROMAGNETICALLY-ACTUATED VIBRATOR COMPRISING A TUNING FORK HAVING A PAIR OF TINES, AND MEANS FOR ACTUATING SAID FORK INCLUDING A TRANSDUCER CONSTITUTED BY A MAGNETIC ELEMENT ATTACHED TO ONE OF SAID TINES AND FORMED BY A CYLINDRICAL CUP HAVING A MAGNETIC ROD SUPPORTED COAXIALLY THEREIN TO DEFINE AN AIR GAP AT THE MOUTH OF SAID CUP, A FIXEDLY-SUPPORTED JULTI-TURN CYLINERICAL COIL RECEIVED WITHIN THE ANNULAR SPACE BETWEEN SAID ROD AND CYLINDER, SAID ELEMENT VIBRTATING AXIALLY RELATIVE TO SAID COIL, SAID ROD BEING TAPERED AND SAID COIL BEING SIMILARLY TAPERED TO PRODUCE THE GREATEST NUMBER OF TURNS WITHIN SAID AIR GAP AT THE POSITION OF MAXIMUM FLUX DENSITY. 